Sensor devices for monitoring the environment of a vehicle are known. They are, for example, used in order to monitor the areas beside and behind a vehicle. This monitoring frequently is done with electromagnetic signals, in particular in the form of radar signals. In the rearward monitoring of the vehicle or in the lateral monitoring of a vehicle two sensors are frequently used. These are customarily mounted at the two transitions of the respective sides of the vehicle towards the rear of the vehicle so that they can monitor the respective side of the vehicle as well as the rear area of the vehicle. These two sensors are connected to one another and configured as a master or slave sensor. This means that one of the two sensors has as the master sensor common functionalities which it makes available to the slave sensor on the opposite side of the vehicle. The known sensors are frequently equipped with a transmitting antenna and three receiving antennas. The receiving antennas of each sensor are preferably coupled to one another in a phase-locked manner so that in a known manner angle measurement of the recognized objects can take place.
It is disadvantageous in the case of the known sensor devices that the two sensors, i.e. the master sensor and the slave sensor, are used exclusively separated from one another. This leads to objects which are moving behind the vehicle preferably at the same speed and/or with the same spacing not being sensable as two separate objects. This is based on the fact that the number of separately recognizable objects is a function of the number of receiving antennas. In particular, this functional relationship is such that half of the number of receiving antennas corresponds to the number of objects which can be sensed separately from one another. Since in the known sensors three receiving antennas are used, this leads to it being theoretically possible to distinguish 1.5 objects separately from one another. Since however either one object or two objects are present, distinguishing the 1.5 objects in mathematics comes to nothing in reality so that separability in known sensor devices is not possible or is possible only to a very limited extent. The separability of the sensors could only be achieved by a structural change in the form of additional receiving antennas. This leads however to greater complexity of the sensor and higher costs.